【单选题】John is a good boy and__________to everyone.
【单选题】John is a good boy because he is ______ late for school.
【简答题】函数f(x)满足条件 f(x+2)= 1 f(x) ,?x∈R ,若f(1)=-5,则f(f(5))=______.
【简答题】函数f(x)对任意实数x满足条件f(x+2)=-f(x),若f(1)=-5,则f[f(5)]=______.
【单选题】SELECT语句中使用( )关键字可以将重复行屏蔽。